Pupil sheet · States and changes of state

States and changes of state — final check

Name ______________________ Date ____________

Work alone, with the lesson closed. Answer every question; there are no hints.

1. evaluate / explain

(a) A pupil writes: “When a gas is squashed, its particles get smaller. When ice melts, the water molecules break apart into hydrogen and oxygen.” Evaluate both statements and correct them. (b) An unknown sample spreads out to fill every closed container it is put in. State its physical state and one other property it has. Describe its particles.

(a) Evaluation and corrections

(b) State, another property and the particles

2. deduce / state / explain

Substance Q is heated at a steady rate. The table shows its temperature. (a) Deduce the melting point and boiling point of Q. (b) State the physical state of Q at 11 minutes. (c) Explain, using particles, why the temperature stays constant from 16 to 20 minutes. (d) Liquid Q in an open dish is kept at 80 °C. Its level slowly falls, with no bubbles. Name this process and give one way it differs from boiling.

Time / minutes	0	2	4	6	8	10	12	14	16	18	20
Temperature / °C	−13	17	17	17	35	62	89	116	118	118	118

(a) Melting point and boiling point

(b) State at 11 minutes

(d) The process and one difference from boiling

3. state / describe / explain

Substance R melts at −95 °C and boils at 56 °C. (a) State the physical state of R at 25 °C and at 80 °C. (b) Gaseous R at 80 °C is cooled slowly to −120 °C. Describe the cooling curve you would expect, naming each change of state and the temperatures where the curve is flat. (c) Explain, using particles, why the temperature stays constant during one of these changes.

(a) State at 25 °C and at 80 °C

(b) The cooling curve and its flat parts